1. Field of the Invention
This invention relates to methods of regenerating a desulfurization sorbent. In another aspect, the invention concerns methods of inhibiting the in situ formation of one or more silicates during the regeneration of a sulfur-laden sorbent composition.
2. Description of the Related Art
The increased global demand for cleaner burning fuels has driven the worldwide effort to reduce the sulfur levels in many hydrocarbon-based fuels, such as gasoline and diesel. Lower-sulfur fuel blends contribute to improved air quality by minimizing the adverse impact on emissions-regulating automotive components, such as, for example, highly sulfur-sensitive catalytic converters. Automobiles operating with inefficient or poisoned catalytic converters emit exhaust containing high levels of non-combusted, heavier-than-methane hydrocarbons, nitrogen oxides (i.e., NOx), sulfur oxides (i.e., SOx), and carbon monoxide. Catalyzed by sunlight, these components react to form ground-level ozone, more commonly referred to as “smog.”
In recent years, the public discussion regarding the reduction of sulfur levels in fuel blends has not focused on whether or not such a reduction should occur, but, rather, has centered on the required level of reduction, as well as the time frame for the implementation of corresponding regulations. Within the last several years, several countries, including China, the United States, Japan, India, Brazil, and the European Union have begun issuing mandates requiring progressively lower sulfur levels (e.g., some less than 10 ppmw) in automotive fuels, including both gasoline and diesel.
These stricter regulations have led oil refiners and other fuel producers/blenders to alter their current fuel production schemes to include processes for desulfurizing the hydrocarbon-containing streams used as blendstocks for producing different types of consumer fuels, including, for example, typical automotive gasolines and diesels, heavy equipment diesel fuels, racing gasolines, aviation gasolines, boat gasolines, and the like. Examples of hydrocarbon streams used as blendstocks to produce these fuels include, but are not limited to, thermally and/or catalytically processed gasolines such as, for example, thermally cracked gasoline, visbreaker gasoline, coker gasoline and catalytically cracked gasoline, which are sometimes collectively referred to as “cracked gasolines.”
Many desulfurization processes and systems employ a catalyst or sorbent to chemically and/or physically remove sulfur-containing compounds from the hydrocarbon stream being desulfurized. Oftentimes, during operation of the desulfurization system, conditions may arise that contribute to the formation of one or more compounds in, on, or within the catalyst or sorbent that adversely affect its desulfurization activity. For example, when the sorbent or catalyst includes a silica-containing compound in association with a metal oxide compound, oxidative regeneration of the sorbent or catalyst can cause the formation of one or more silicates in, on, and/or within the sorbent or catalyst. Silicates are generally inert, but can occupy the active sites on the catalyst or sorbent, thereby reducing the desulfurization activity of the catalyst or sorbent. Because silicates cannot be removed by conventional oxidative regeneration methods, catalyst or sorbent that has been deactivated by the formation of silicates must generally be deinventoried from the desulfurization unit and completely replaced. To avoid the high operating and lost production costs associated with such a catalyst or sorbent replacement, refiners have long desired a method of minimizing the formation of silicates on desulfurization catalyst and/or sorbent.